1. Field of the Invention
The present invention relates to a sensor, a phase separation detecting system and a phase separation detecting method.
2. Description of the Related Art
Alcohol containing fuels absorb moisture in the air. Thus, the water concentration in alcohol containing fuels increases. A phenomenon called phase separation, meaning that gasoline and water are separated, is caused when the water concentration in the alcohol containing fuel reaches a predetermined concentration or greater. When phase separation is caused, alcohol is inevitably trapped into a water layer because of its highly hydrophilic properties. In this case, chances are that the octane number of the fuel or the vapor pressure decreases, and accordingly, the function of an engine or a fuel system degrades.
The amount of water that causes the phase separation varies in accordance with temperature and the alcohol concentration in the alcohol containing fuel. Further, the alcohol concentration in the alcohol containing fuel varies depending on regions. Thus, it is difficult to accurately detect a possibility of occurrence of the phase separation only by simply detecting the amount of water contained in the alcohol containing fuel.
In view of the above, a control device for alcohol blended fuel, described in Japan Laid-open Patent Application JP-A-2007-262915, is configured to calculate the amount of water containable in the fuel without causing the phase separation with use of an ethanol concentration sensor and an outdoor temperature sensor. Further, the possibility of occurrence of the phase separation is evaluated by comparing a calculated acceptable amount of water and an amount of water measured by a WIF (water-in-fuel) sensor.
The control device described in JP-A-2007-262915 at least requires the ethanol concentration sensor, the outdoor temperature sensor, and the WIF sensor in order to detect the possibility of occurrence of the phase separation. Thus, the control device includes the drawbacks of being structurally complicated and increasing the manufacturing cost.
It should be noted that Paragraph [0051] in JP-A-2007-262915 describes that the WIF sensor may not be provided if it is possible to estimate a boundary of occurrence of the phase separation (phase separation line) with a predetermined accuracy. However, the control device described in JP-A-2007-262915 cannot detect the amount of water contained in the alcohol containing fuel when it is not provided with the WIF sensor. Thus, the accuracy in detecting the possibility of occurrence of the phase separation remarkably degrades. Further, JP-A-2007-262915 discloses the condition “if it is possible to estimate a boundary of occurrence of the phase separation (phase separation line) with a predetermined accuracy”. However, it is difficult to estimate the boundary in the first place.
On the other hand, when the water concentration in the alcohol containing fuel increases even though it is not high enough to cause the phase separation, some functional disorder could be caused by a change in shape of a fuel-based material due to swelling, corrosion, or formation of extraneous substances due to extraction. The amount of water, thus affecting such a function, is not an absolute amount but an amount relative to the amount of water causing the phase separation. Therefore, similarly to detecting the possibility of occurrence of the phase separation, it is difficult to accurately detect the possibility of occurrence of the above-described functional disorder only by simply detecting the amount of water contained in the alcohol containing fuel. Consequently, it has been demanded to accurately detect, with a simple structure, a ratio of an actual amount of water to the amount of water causing the phase separation in an alcohol containing fuel.